This invention relates generally to remote control systems and particularly to remote control transmitters for use in controlling a plurality of functions in a number of controlled devices. The disclosure of the co-pending application mentioned above briefly describes the development of wireless remote control systems for remotely controlling apparatus such as model airplanes, toy automobiles, a variety of industrial machines and home entertainment devices. The systems of particular interest as those related to control of home entertainment devices, specifically those used for controlling a television receiver (TV), a video cassette recorder (VCR) and many other entertainment or information media useful with a television receiver. Examples of these are teletext systems (TEXT) for bringing a wide variety of information to the home, cable television systems and wireless telephone systems which enable telephone communications through the medium of a television receiver. Specifically, an integrated circuit (IC) is provided in a hand-held transmitter with a code signal generator and memory for developing and transmitting a plurality of infra-red coded output signals as a function of closure of keys or buttons on a matrix keyboard. The keyboard is conventional and is of the generally well known calculator type that completes an X-Y connection with each key closure. Specifically, a 32 key keyboard has eight "X" positions and four "Y" positions. The above application describes a Y5 port on the IC for selecting a specific memory "page" from among the eight pages provided as a function of the particular X port to which the Y5 port is connected. Any of the eight pages of memory may be accessed by hard-wiring the Y5 port to different ones of the X ports. A mask program option is also provided to enable the keyboard to access more than one memory page. This option is selected by a "default" condition, where there is no connection between Y5 and the X ports. An X-Y discriminator generates the device or memory page address code in accordance with the X-Y closures based upon the predetermined correlation pattern built into the discriminator. Thus, while a single transmitter is capable of accessing different memory pages, the mask option is not changeable without redoing the IC.
The advantages of the above-described scheme for a home entertainment equipment manufacturer are many. While not a critical requirement, a highly desirable attribute for remotely controllable devices produced by a manufacturer is that the control transmitters therefor, be capable of controlling the same function in the same type devices produced over the years. Thus, for example, if one purchases a 1983 Zenith Radio Corporation infra-red remote control TV, its control transmitter would also control the same functions in a 1982 Zenith infra-red remote control TV, in a 1984 Zenith remote control TV, etc. Similarly, remotely controllable video cassette recorders would have this same "forward and backward compatibility". Quite obviously such an attribute has great appeal to users.
There is another, equally important, reason that is grounded on the likelihood of a user owning more than one remotely controllable device, and the probability that such devices would be located in the same general area. For example, it is not at all unusual for a user to have a remotely controlled TV and a remotely controlled VCR, made by the same manufacturer, positioned adjacent to each other. In addition other special television services, options and features such as, for example, teletext, cable and wireless telephone may be available. The user may even have a projection type TV in which the viewing screen is raised and lowered by remote control. It can readily be seen that in such an environment, it is mandatory that control signals for the TV not operate the VCR, etc.
With the transmitter IC described in the above application, 256 different code combinations (memory locations) are available with an 8.times.4 keyboard matrix. Thus by using the Y5 teaching and a separate memory page for the different control codes for each device, a manufacturer may produce individual remote control transmitters for a variety of devices with complete independence therebetween, since each transmitter would only access the particular memory page corresponding to its associated controlled device.
For the further convenience of users, manufacturers are incorporating multi-device control functions in a single transmitter. As suggested in the co-pending application, this may be accomplished by providing a separate multi-pole switch on the transmitter for switching the Y5 connection among the X ports to access the memory page for the particular device to be controlled. A major drawback is that the entire keyboard is thereby switched and failure to note the position of the device switch could have surprising and sometimes unusual results. For example, one could easily raise or lower a projection screen while intending to perform a totally different function with a VCR, since the selected device switch position results in the entire keyboard accessing the corresponding device memory page. Thus if the device switch was on TV, but the user thought it was on VCR, the TV functional response obtained by a key operation could be disconcerting, at least. Another drawback is that the graphics would often need double or triple labeling of the keys.
As noted, it has been found most convenient to store the digital codes of the control functions applicable to a particular device in a single memory page, primarily for the above-mentioned reasons of compatibility. What is desired and needed in the art is a mechanism for enabling certain keys on the keyboard to be "redefinable" among a number of devices and others to be "dedicated" to a particular device. The redefinable keys would control the same function in a group of different devices depending upon the position of a device switch, whereas the dedicated keys would only control their associated devices, irrespective of the position of the device switch. This is accomplished in the invention by providing two independent contact closures or switches for each key operation, one for selecting the device to be controlled (memory page) and the other for defining the control function. Certain keys for common functions are redefined with a device switch, while the other keys are unique to a particular device. The invention yields attractive benefits in cost and packaging and retains the advantages of compatibility and elimination of unanticipated functional responses resulting from user errors. The packaging benefit of the invention contributes to keeping the transmitter uncluttered, enables convenient grouping of functions on the transmitter and materially simplifies the transmitter graphics--all of which should contribute to enhanced user acceptance of such combination transmitters.